A magnetic disk drive includes a disk-shaped recording medium disposed in a casing, that is, a magnetic disk and a magnetic head that reads and writes information from/to the magnetic disk. The magnetic head includes, for example, a recording head and a read head (reproducing element). The recording head includes a main magnetic pole that generates a recording magnetic field, a write shield, and side shields that face each other with a gap between the main magnetic pole.
In such a recording head, recording resolution (recording density) is largely influenced by a distance (gap length) between the main magnetic pole and the shield. With increasing recording density, the gap length tends to become smaller. However, when the gap length becomes smaller, the write shield can be magnetically saturated due to the magnetic field generated from the main magnetic pole. As a result, the write shield does not function effectively as a shield. In this case, the recording resolution and the recording density of the recording head are adversely affected.